Over the last decade, there has been a considerable transformation in the solvent-borne industrial coatings market. Major developments have taken place in water based coatings technology, which has now expanded from the consumer house paint market into industrial sectors. Increasingly stringent VOC regulations have led to the development of a more viable water based alternative to solvent borne technology. However, some limitations still exist, particularly with the key characteristics of chemical and abrasion resistance in coating performance.
Alongside the advances in water based technology, has been the development of high solids coatings. These are usually formulated with lower molecular weight components to achieve the lowest possible viscosity with the minimum use of solvent. However, there is a limit to molecular weight reduction, as this can lead to problems associated with loss of coating performance.
An example of a market that has seen the trends as described above is 2-pack polyurethane coatings. Typically, these systems are comprised of an acrylic (or acrylic and polyester) polyol and an HDI-based polyisocyanate. These form polyurethanes possessing unique performance properties including excellent chemical resistance and weather exposure as well as good abrasion resistance. One possible solution to maintaining the coating benefits of solvented systems, whilst reducing the VOC, is to incorporate a reactive diluent.
Incozol LV – Reactive Diluent
Incozol LV is a low viscosity bis-oxazolidine reactive diluent designed as a co-reactant in polyurethane coatings to achieve low VOC. Incozol LV is comprised of two oxazolidine rings (five membered heterocylic rings containing nitrogen and oxygen) linked by a carbonato bridge, which affords low viscosity by restricting intermolecular hydrogen bonding.
Chemistry of Oxazolidine Diluents
The ability of Incozol LV to co-react into the polyurethane backbone of the coating is activated by the ring opening hydrolysis of the two oxazolidine rings, resulting from the reaction of water present as moisture contamination in both the solvent and polyol components. Moisture in the atmosphere during spraying application also aids the activation of the oxazolidine rings. Consequently, the inclusion of Incozol LV has the dual benefit of scavenging moisture, as well as lowering the VOC. Polyurethane coatings can be adversely affected by moisture, through the reaction of water with the polyisocyanate component, forming carbon dioxide gas. This can often result in pinhole defects in the coating or hazing problems with clear lacquer finishes. Hence, pre-mixing Incozol LV with the polyol and solvent component to scavenge the moisture prior to polyisocyanate mixing is clearly an advantage towards improving the coating. Indeed, repeated opening of containers will serve to further activate the oxazolidine prior to hardener (polyisocyanate) mixing.
Activation of Incozol LV results from the hydrolytic ring opening of the oxazolidines yielding hydroxyl and amino functionality on each ring. Consequently, with Incozol LV, four sites (two hydroxyl and two amino) are available for reaction with polyisocyanate.
Features & Benefits
• Good polyol and solvent compatibility
• Low intrinsic viscosity - 50 mPas @ 20ºC
• Reasonably high equivalent weight - 86 (functionality of 4)
• Low colour - essential for clear lacquer finishing
• Workable pot life and cure response
• No adverse effect on the coating properties including film hardness development and resistance, gloss and weathering properties
Typical Applications
• One- and two-component polyurethanes
• Low VOC paints and varnishes
• High build paints
• Elastomers
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